1. Field of the Invention
The present invention relates to a polishing pad and a method of manufacturing the same, and more particularly, to a polishing pad containing embedded liquid microelements and a method of manufacturing the same.
2. Description of the Related Art
Chemical mechanical planarization/polishing (CMP) has been used for global planarization of semiconductor devices and has become important with tendencies to increase the diameter of a wafer, a high integration density, a micro line width, and a multilayer wiring structure.
In a CMP process, under a state in which the surface of a wafer to be processed is in contact with a polishing pad due to a predetermined down pressure applied to the wafer, the wafer and the polishing pad are moved relative to one another while a polishing slurry is supplied to the contact therebetween so that physical abrasion is provoked by abrasive particles contained in the polishing slurry and the protrusions of the polishing pad, and simultaneously chemical abrasion is provoked by chemical components within the polishing slurry. The performance of such a CMP process is estimated from a polishing speed and the flatness of a wafer and depends on the conditions of CMP equipment, the performance of a polishing slurry, and the performance of a polishing pad.
In particular, it is necessary that a polishing pad's surface directly contacting a wafer is saturated with a polishing slurry so that the polishing slurry flows smoothly. Polishing pads, which include a polymeric matrix impregnated with a plurality of hollow polymeric microelements and/or micro hollow polymeric bundles having a fine-textured structure to collect and supply a polishing slurry for the purpose of allowing the polishing slurry to flow efficiently, are disclosed in U.S. Pat. No. 5,578,362 and Korean Patent Publication Nos. 2001-2696 and 2001-55971.
However, the polishing pad disclosed in U.S. Pat. No. 5,578,362 includes two elements having different hardnesses, i.e., a polymeric matrix and hollow polymeric microelements, on its surface. Due to a difference in hardness, the polishing pad's surface has different supporting forces against a friction pressure during a polishing operation, which results in a difference in the amount of abrasion on the polishing pad's surface. This difference in abrasion leads to non-uniform supply and distribution of a polishing slurry, which may result in non-uniform polishing on a wafer. Moreover, the polymeric microelements existing on the polishing pad's surface have a high hardness, which may cause the surface of the wafer to be scratched during the polishing operation. A material in a powder state having a low specific gravity is used for the polymeric microelements. Accordingly, when mixing the powder with a material for the polymeric matrix by agitating them, the powder has poor workability. In addition, non-uniform dispersion of powder results in non-uniform distribution of pores in a manufactured pad. Then, a polishing slurry cannot be uniformly carried, so polishing uniformity across a wafer is decreased. A lump of powder that is not appropriately dispersed may damage the surface of a wafer. A polishing pad including hollow polymeric microelements and micro hollow polymeric bundle particles, disclosed in Korean Patent Publication No. 2001-55971, also has these problems.
In the meantime, a polishing pad disclosed in Korean Patent Publication 2001-2696 includes only micro hollow polymeric bundle particles having an average diameter of 0.4-2 μm, so the amount of a collected polishing slurry is small. A small amount of a polishing slurry decreases a polishing speed. The same problem occurs in a polishing pad mainly including micro hollow polymeric bundles, which is disclosed in Korean Patent Publication No. 2001-55971.
It is important to accurately and quickly measure the flatness of a wafer during a polishing operation. In U.S. Pat. Nos. 5,893,796 and 6,171,181, polishing pads suitable for optically measuring the flatness of a wafer in situ are disclosed. However, in a polishing pad disclosed in U.S. Pat. No. 5,893,796, a transparent plug is inserted into a pad in order to form a transparent window capable of transmitting a light beam. For this, manufacturing processes of forming an aperture in the pad and fixing the transparent plug in the aperture with an adhesive are additionally required. In U.S. Pat. No. 6,171,181, a transparent region is formed in a pad by more quickly solidifying a predetermined region than any other region in a mold. This requires a special mold in which temperature can be differently adjusted depending on portions, and therefore, manufacturing cost is increased.